Today""s soldier is confronted with the possibility of coming in contact with deadly, invisible chemical or biological weapons of mass destruction. Lethal concentrations of biological weapons, in particular, are so minute that advance detection has been nearly impossible, particularly on the battlefield. In theory, any airborne substance, including chemical and biological warfare agents, can be detected by interrogation with terahertz electromagnetic waves. Accurate identification of substances by this method, however, requires precise measurement over a wide bandwidth of the amplitude and phase of the energy emitted from the interrogated object. To date, there have been no practical, high-sensitivity, broadband, terahertz detectors capable of detecting the amplitude and phase of terahertz electromagnetic waves. The present invention provides remarkably high sensitivity, ultra-wide bandwidth optical detection of both the amplitude and phase of a terahertz frequency or below electric field, and will enable detection in the field of trace amounts of chemical and biological warfare agents. The invention has numerous other civilian and military applications, including ultra-wide bandwidth wireless communication, optical sampling of submillimeter wave signals for optical A-D conversion, covert communications, and measurement of nonequilibrium transport in optoelectronic devices.
The invention will enable one to use the polarization properties of incident light to achieve higher sensitivity through background-free or polarization-sensitive detection. It is capable of better sensitivity than a conventional multiple quantum well detector which is hampered by the small amplitude modulation depth of the excitonic electroabsorption super-imposed upon a background of transmitted near-infrared light. Moreover, because the response time of the excitonic electroabsorption is only limited by the inverse of the exciton linewidth in the presence of the applied electric field, the invention also possesses wider bandwidth than other high sensitivity detectors such as photoconductive dipole antennas, the bandwidth of which is limited by the photogenerated carriers in the photoconductor.